Method and system for inspecting an euv mask

ABSTRACT

A structure for grounding an extreme ultraviolet mask (EUV mask) is provided to discharge the EUV mask during the inspection by an electron beam inspection tool. The structure for grounding an EUV mask includes at least one grounding pin to contact conductive areas on the EUV mask, wherein the EUV mask may have further conductive layer on sidewalls or/and back side. The inspection quality of the EUV mask is enhanced by using the electron beam inspection system because the accumulated charging on the EUV mask is grounded. The reflective surface of the EUV mask on a continuously moving stage is scanned by using the electron beam simultaneously. The moving direction of the stage is perpendicular to the scanning direction of the electron beam.

CLAIM OF PRIORITY

This application is a continuation of pending U.S. application Ser. No.14/575,102 filed Dec. 18, 2014, which is a continuation-in-part of U.S.application Ser. No. 14/039,939 filed Sep. 27, 2013, which is acontinuation of U.S. application Ser. No. 13/112,536 filed May 20, 2011,now U.S. Pat. No. 8,575,573 issued Nov. 5, 2013, the entire disclosuresof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for inspecting an EUV mask byusing a charged particle beam, and more especially, to a method forinspecting the EUV mask with grounding means such that the EUV mask canbe continuous scanned by electron beams.

2. Background of the Related Art

Optical inspection of a mask is based on a comparison of the lightsignals in the patterned regions relative to the non-patterned regions.A high contrast is necessary in order to achieve sufficient sensitivityfor defect detection. The transmissive masks used in DUV (deep UltraViolet) lithography can be inspected without difficulty since thecontrast between the opaque regions and the clear regions is high atUV/DUV wavelengths. However, it is difficult to inspect the reflectivemasks, the EUV mask for example, used in EUV lithography since not onlythe contrast between the absorber region and the mirror region is low atUV/DUV wavelengths, but also wavelength of the UV/DUV is too lengthy toinspect EUV mask.

Now, a charged particle beam inspection system, an electron beam(E-beam) inspection tool, accordingly, is developed to inspect the EUVmask. However, accumulated charging on EUV mask will induce inspectionissue while the EUV mask is inspected by the E-beam inspection tool.This issue will not happen to silicon wafer because silicon wafer can begrounded. Substrate of the EUV mask is dielectric, and cannot begrounded.

Furthermore, if the EUV mask on a moving stage is scanned continuouslyby the electron beam and charges are accumulated on the surface of theEUV mask without grounding, the contrast and intensity of the scannedimages at different areas would not be consistent or equal during theinspection process. In other words, the electron beam scanning overdifferent regions of the EUV mask would cause dwell times in order tomake the images have better quality and consistent contrast andintensity during the inspection operation. The inspection speed and thethroughput would be influenced greatly.

SUMMARY OF THE INVENTION

In order to solve the foregoing problems, one object of this inventionis to provide a structure to discharge the EUV mask during inspection byan E-beam inspection tool, so that non accumulated charging is on theEUV mask during E-beam inspecting to enhance the inspection quality.

Accordingly, one embodiment of the present invention provides astructure for discharging EUV mask including: means for conductingcharge on an EUV mask in inspecting the EUV mask by using a chargedparticle beam inspection system; and a grounding pin to contact themeans.

Another embodiment of the present invention provides a structure fordischarging EUV mask including: at least a conductive layer on one sideof an EUV mask; and a grounding pin to contact the conductive layer, sothat charge on a reflective surface of the EUV mask is grounded throughthe conductive layer to the grounding pin.

Another embodiment of the present invention provides a structure fordischarging EUV mask including: a first conductive layer on one side ofan EUV mask; a second conductive layer on a surface opposite to areflective surface of the EUV mask; and a grounding pin to contact thesecond conductive layer, so that charge on the reflective surface of theEUV mask is grounded through the second conductive layer to thegrounding pin.

Another embodiment of the present invention provides an electron beaminspection system for inspecting an EUV mask including: an electron gunfor providing electron beam; a lens for focusing the electron beam onthe EUV mask; a detector for receiving signal electron emanating fromthe EUV mask; and means for discharging the EUV mask during the EUV maskis inspected.

Another embodiment of the present invention provides a method forinspecting an EUV mask by using a charged particle beam including:grounding the EUV mask; moving a stage, for supporting the EUV mask,continuously and scanning a surface of the EUV mask by using the chargedparticle beam simultaneously; and receiving signal electrons emanatedfrom the surface of the EUV mask.

Another embodiment of the present invention provides a system forinspecting an EUV mask including: a source for providing an electronbeam; an objective lens for focusing the electron beam on a surface ofthe EUV mask; a detector for receiving signal electrons emanated fromthe surface of the EUV mask; a stage for supporting the EUV mask; andmeans for grounding the EUV mask, wherein the surface of the EUV mask isscanned by the electron beam when the stage moves continuously,

Another embodiment of the present invention provides a method forinspecting an EUV mask by using a charged particle beam, which comprisessteps of grounding the EUV mask, moving a stage continuously andscanning a reflective surface of the EUV mask by using the chargedparticle beam simultaneously, and receiving signal electrons emanatedfrom the surface of the EUV mask, wherein the stage supports the EUVmask.

The charged particle beam can be an electron beam. A stage's movingdirection is perpendicular to a scanning direction of the electron beam.The EUV mask can be inspected by a low voltage scanning electronmicroscope. The step of grounding the EUV mask can be performed byslightly contacting a grounding pin to the reflective surface of the EUVmask.

The step of grounding the EUV mask can be performed by contacting agrounding pin to a back surface of the EUV mask and electricallyconnecting to the reflective surface of the EUV mask. The grounding pincan contact the back surface of the EUV mask slightly.

The step of grounding the EUV mask can be performed by slightlycontacting a grounding pin to a conductive layer on one side wall of theEUV mask. A trench can be formed in the side wall of the EUV mask. Theconductive layer can be coated within the trench.

Another embodiment of the present invention provides a system forinspecting an EUV mask, which comprises a source for providing anelectron beam, an objective lens for focusing the electron beam on areflective surface of the EUV mask, a detector for receiving signalelectrons emanated from the surface of the EUV mask, a stage forsupporting the EUV mask, and means for grounding the EUV mask, whereinthe surface of the EUV mask is scanned by the electron beam when thestage moves continuously.

A stage's moving direction is perpendicular to a scanning direction ofthe electron beam. The system can be a low voltage scanning electronmicroscope. The means for grounding the EUV mask can include a groundingpin slightly contacting the reflective surface of the EUV mask.

The means for grounding the EUV mask can include a grounding pincontacting a back surface of the EUV mask, and a conductive layer can beon the back surface of the EUV mask and electrically connecting to thereflective surface of the EUV mask. The grounding pin can contact theback surface of the EUV mask slightly.

The means for grounding the EUV mask can include a grounding pincontacting a conductive layer on one side wall of the EUV mask. A trenchcan be formed in the side wall of the EUV mask. The conductive layer canbe coated within the trench.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a configuration of an EUVmask;

FIG. 2 illustrates a vertical view of a configuration of an EUV mask;

FIG. 3a and FIG. 3b illustrate the diagrams about the working status ofthe EUV mask and the grounding pin in accordance with the firstembodiment of the present invention;

FIG. 4 illustrates a diagram about a configuration of the EUV mask andthe slider;

FIG. 5 illustrates a diagram about a configuration of the EUV mask andthe electron gun;

FIG. 6a and FIG. 6b illustrate the diagrams about the working status ofthe EUV mask and the grounding pin in accordance with the secondembodiment of the present invention;

FIG. 7a and FIG. 7b illustrate the diagrams about the working status ofthe EUV mask and the grounding pin in accordance with the thirdembodiment of the present invention;

FIG. 8 illustrates a first embodiment of the grounding pin controllingstructure;

FIG. 9a , FIG. 9b and FIG. 9c illustrates a second embodiment of thegrounding pin controlling structure;

FIG. 10a , FIG. 10b and FIG. 10c illustrates a third embodiment of thegrounding pin controlling structure;

FIG. 11 illustrates a cross-sectional view of a configuration of anotherEUV mask;

FIG. 12a and FIG. 12b illustrate the diagrams about the working statusof the EUV mask and the grounding pin in accordance with the fourthembodiment of the present invention;

FIG. 13a and FIG. 13b illustrate the diagrams about the working statusof the EUV mask and the grounding pin in accordance with the fifthembodiment of the present invention;

FIG. 14 illustrates the diagrams about the working status of the EUVmask and the grounding pin in accordance with the sixth embodiment ofthe present invention;

FIG. 15a and FIG. 15b respectively illustrates a cross-sectional viewand a vertical view of a configuration of another EUV mask;

FIG. 16 illustrates a diagram of a conductive holder clamping the EUVmask in accordance with another embodiment of the present invention;

FIG. 17 illustrates a vertical view of a configuration of another EUVmask; and

FIG. 18 illustrates a vertical view of a configuration of another EUVmask.

FIG. 19 is a flow chart illustrating a method for inspecting an EUV maskby using a charged particle beam in accordance with one embodiment ofthe present invention.

FIG. 20 shows an embodiment of a low voltage scanning electronmicroscope; and

FIG. 21 shows a schematic diagram of a structure for an electron beaminspection system processing continuous scanning on an EUV mask inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a cross-sectional view of a configuration of an EUVmask. The EUV mask 10 includes a substrate 12, an EUV absorption layer14 on the substrate 12 and a patterned reflective surface 16 formed onthe absorption layer 14. Referring to FIG. 2 simultaneously, thepatterned reflective surface 16 has a peripheral area 161 without anypattern and a middle area 162 with a plurality of pattern openings 163thereon. Here, the patterned reflective surface of the EUV mask may beholes, circuits, devices, or any combination thereof. In one embodiment,the reflective layer, made of the same or different metals, is formed ona substrate of the EUV mask, and portion of the plurality of patternsmay distribute on the reflective layer. A structure for discharging EUVmask includes: means for conducting charge on the EUV mask 10 ininspecting the EUV mask 10 by using a charged particle beam inspectionsystem; and a grounding pin (shown in following diagrams) to contact themeans. In one embodiment, the grounding pin is used to contact a portionof the peripheral area 161 of the patterned reflective surface 16, whichis made of electrical conductive materials, or electrical semiconductivematerials, and thereby grounds charges on the reflective surface 16 ofthe EUV mask 10.

FIG. 3a and FIG. 3b illustrate the diagrams about the working of the EUVmask and the grounding pin in accordance with the first embodiment ofthe present invention. In the first embodiment, the structure 20 fordischarging EUV mask further includes a slider 22, a spring 24 and anarm structure 26. The slider 22 has a top surface 28 divided into a flatarea 281 and a downward-tilted area 282. One end of the spring 24connects to a back side 221 of the slider 22 and the other end of thespring 24 is fixed. The arm structure 26 is above the slider 22 and thearm structure 26 includes a body 261, the grounding pin 262 on a frontend of the body 261 and a prop 263 connecting to the body 261. As shownin FIG. 3a , when the EUV mask 10 is under the ungrounded status, theprop 263 of the arm structure 26 contact the flat area 281 of the slider22 and the grounding pin 262 is far away from the EUV mask 10. When theEUV mask 10 moves toward a front side 222 of the slider 22 to contactand push the slider 22 back, as shown in FIG. 3b , the prop 263 movesalong the top surface 28 of the slider 22 and then contacts thedownward-tilted area 282, and therefore the body 261 of the armstructure 26 tilts and the grounding pin 262 contacts the reflectivesurface 16 of the EUV mask 10.

As shown in FIG. 4, the slider 22 has a gap 30 on the front side 222 ofthe slider 22 for holding one corner of the EUV mask 10, so that theslider 22 may fix the EUV mask 10, as the EUV mask 10 contacts with theslider 22 during the EUV mask 10 is grounded by the grounding pin 262(shown in FIG. 3a , FIG. 3b ) and inspected by charged particle beaminspection system, in which the electron gun 32 for providing electronbeam is above the EUV mask 10, as shown in FIG. 5.

FIG. 6a and FIG. 6b illustrate the diagrams about the working status ofthe EUV mask and the grounding pin in accordance with the secondembodiment of the present invention. In the second embodiment, as shownin FIG. 6a and FIG. 6b , the structure 40 for discharging EUV maskfurther includes a gripper unit 42, an arm structure 44, a reciprocatingmember 46 and two resilient members 48, 48′.

The gripper unit 42 includes a head portion 421, a base portion 422 anda first rolling member 423 set at a bottom end of the base portion 421.The gripper unit 42 is used for fixing the EUV mask 10 in place, forexample but not limited to, being held tight or to be released, throughrotation of the gripper unit 42 about a first pivot 424 substantiallyparallel with a first center axis of the first rolling member 423.

The arm structure 44 is configured near or opposite the gripper unit 42.The arm structure 44 includes a body 441, the grounding pin 50 on a topend of the body 441 and a second rolling member 442 set at a bottom endof the body 441. The grounding pin 50 may reciprocate to contact the EUVmask 10 and leave the EUV mask 10 through rotation of the body 441 abouta second pivot 443 substantially parallel with a second center axis ofthe second rolling member 442.

The two resilient members are one first resilient member 48 and onesecond resilient member 48′ each with one end being fixed, andrespectively with the other ends being connected to head portion 422 ofthe gripper unit 42 and to the body 441 of the arm structure 44 forrespectively providing a first force to the gripper unit 42 toward afirst direction 52 and a second force to the body 441 of the armstructure 44 toward a second direction 54.

The reciprocating member 46 is configured for causing the first rollingmember 423 and the second rolling member 442 to rotate. Thereciprocating member 46 includes a fix end 461 and a mobile end 462pivoting the fixed end 461. The first rolling member 423 and the secondrolling member 442 may be in contact with reciprocating member 46 androll freely on the surface of the reciprocating member 46. Here, thereciprocating member 46 is tilted by pushing up and pulling down themobile end 462 of the reciprocating member 46 pivoting the fixed end 461of the reciprocating member 46, which results in the first rollingmember 423 and the second rolling member 442 rolling on thereciprocating member 46.

As shown in FIG. 6a , when the reciprocating member 46 works to make thefirst rolling member 423 to move substantially along the first direction52 and the second rolling member 442 move substantially along the seconddirection 54, the head portion 422 of the gripper unit 42 moves towardthe opposite direction of the first direction 52 and the grounding pin50 moves toward the opposite direction of the second direction 54 sothat the head portion 422 and the grounding pin 50 are led away from theEUV mask 10. As shown in FIG. 6b , when the reciprocating member 46works to leave the first rolling member 423 and the second rollingmember 442, the head portion 422 of the gripper unit 42 moves toward thefirst direction 52 by means of the first force of the first resilientmember 48 and an upper portion of the arm structure 44 moves toward thesecond direction 54 by means of the second force of the second resilientmember 48′, so that the head portion 422 is therefore led toward theedge of the EUV mask 10 and in the end to abut against the EUV mask 10,and the grounding pin 50 contacts the reflective surface 16 of the EUVmask 10. Here, the head portion 422 of the gripper unit 42 is used topush tighter against the EUV mask 10 to hold it fixed in position duringthe EUV mask 10 is grounded by the grounding pin 50 and inspected by thecharged particle beam inspection system.

FIG. 7a and FIG. 7b illustrate the diagrams about the working status ofthe EUV mask and the grounding pin in accordance with the thirdembodiment of the present invention. In the third embodiment, thestructure for discharging EUV mask further includes the foregoinggripper unit 42, the foregoing first resilient member 48, the foregoingreciprocating member 46 and a grounding pin controlling structure 60.Here, the structures, the connection relations and the operation of thegripper unit 42, the first resilient member 48 and the reciprocatingmember 46 are described in the second embodiment as shown in FIG. 6a andFIG. 6b , wherein the head portion 422 of the gripper unit 42 is used topush tighter against the EUV mask 10 to hold it fixed in position duringthe EUV mask 10 is grounded by the grounding pin 50. The grounding pincontrolling structure 60 includes a hollow cylinder 62 and a column 64passing through the hollow cylinder 62. A grounding pin 50 is arrangedon a top surface of the column 64 and the position of the grounding pin50 is changed by moving the column 64. As shown in FIG. 7a , when thegripper unit 42 pushes tighter against the EUV mask 10, the column 64moves down and the grounding pin 50 contacts the reflective surface 16of the EUV mask 10. As shown in FIG. 7b , when the gripper unit 42releases the EUV mask 10, the column 62 moves up and the grounding pin50 is far away from the EUV mask 10.

In first embodiment of the grounding pin controlling structure, thegrounding pin controlling structure 60 includes a hollow cylinder 62 anda column 64 passing through the hollow cylinder 62, wherein the column64 has an interior room 641, as shown in FIG. 8. A first rod 66 with thespiral shells 661 on the outer surface and a second rod 68 with thesawtooth 681 on the outer surface are configured in the interior room641, wherein the spiral shells 661 and the sawtooth 681 are engaged witheach other. A first pushing shaft 70 is connected to the bottom of thecolumn 64 and a second pushing shaft 72 is connected to the bottom ofthe second rod 68 and passes through the bottom of the column 64. Oneend of a connection rod 74 is connected to the top of the first rod 66,and another end of the connection rod 74 is connected with a groundingpin 50. During the inspection of the EUV mask 10, the column 64 movesdown in relative to the hollow cylinder 62 (shown in FIG. 7a ), so thatthe grounding pin 50 contacts the reflective surface 16 of the EUV mask10 (shown in FIG. 7a ). After the inspection of the EUV mask 10, thecolumn 64 moves up continuously in relative to the hollow cylinder 62(shown in FIG. 7b ) so that the grounding pin 50 rise, wherein thesecond rod 72 also moves up to drive the first rod 66 to rotate with thesawtooth 681 engaging with the spiral shells 661, so that the groundingpin 50 may rise and deflect, simultaneously to be far away from the EUVmask.

In second embodiment of the grounding pin controlling structure, asshown in FIG. 9a , the grounding pin controlling structure 60 includes ahollow cylinder 62 and a column 64 passing through the hollow cylinder62. As shown in FIG. 9b , the hollow cylinder 62 has two oppositetrenches 80 formed on an inner surface 621 of a side wall 622 of thehollow cylinder 62, wherein each trench 80 has a lengthwise ditch 801and an upward-tilted ditch 802 connecting to a top end of the lengthwiseditch 801. Correspondingly, as shown in FIG. 9c , the column 64 has twoopposite protrusions 82 on an outer surface of the column 64 and theprotrusions 82 are respectively arranged within the opposite trenches80, as shown in FIG. 9a to move along the lengthwise ditch 801 and theupward-tilted ditch 802. During the inspection of the EUV mask, thecolumn 64 moves down in relative to the hollow cylinder 62 (shown inFIG. 7a ), so that the grounding pin 50 contacts the reflective surface16 of the EUV mask 10 (shown in FIG. 7a ). After the inspection of theEUV mask 10, the column 64 moves up continuously in relative to thehollow cylinder 62, wherein the column 64 moves up straightly and thendeflects as protrusions 82 moves along the lengthwise ditch 801 and thenthe upward-tilted ditch 802, so that the grounding pin 50 is far awayfrom the EUV mask 10.

In third embodiment of the grounding pin controlling structure, as shownin FIG. 10a , the grounding pin controlling structure 60 includes ahollow cylinder 62 and a column 64 passing through the hollow cylinder62. As shown in FIG. 10b , the hollow cylinder 62 has two oppositetrenches 84 passing through a side wall 622 of the hollow cylinder 62,wherein each trench 84 has a lengthwise ditch 841 passing through theside wall 622 and a upward-tilted ditch 842 passing through the sidewall 622 and connecting to a top end of the lengthwise ditch 841.Correspondingly, as shown in FIG. 10c , the column 64 has two oppositebranch structures 86 including at least two horizontal rods 861respectively, and the branch structures 86 are respectively arrangedwithin the opposite trenches 84, as shown in FIG. 10a , to move alongthe lengthwise ditch 841 and the upward-tilted ditch 842. During theinspection of the EUV mask, the column 64 moves down in relative to thehollow cylinder 62 (shown in FIG. 7a ), so that the grounding pin 50contacts the reflective surface 16 of the EUV mask 10 (shown in FIG. 7a). After the inspection of the EUV mask 10, the column 64 moves upcontinuously in relative to the hollow cylinder 62, wherein the column64 moves up straightly and then deflects as the branch structures 86moves along the lengthwise ditch 841 and the upward-tilted ditch 842, sothat the grounding pin 50 is far away the EUV mask 10.

In the foregoing embodiments, the grounding pin 50 is used to contactthe reflective surface 16 which is formed on the top surface of the EUVmask 10. Nevertheless, the position that the grounding pin contacts withmay be changed. As shown in FIG. 11, a first conductive layer 90 and asecond conductive layer 92 may respectively be coated on the side of theEUV mask 10 and coated on the bottom surface, which is opposed to thereflective layer 16, of the EUV mask 10. The reflective surface 16, thefirst conductive layer 90 and the second conductive layer 92 areelectrically connected, so that the foregoing grounding pin 50 may beused to contact the second conductive layer 92, so that charge on thereflective surface 16 of the EUV 10 mask is grounded through the firstconductive layer 90 and the second conductive layer 92 to the groundingpin 50. The coated first conductive layer 90 and the second conductivelayer 92 may be Al, Cr, Ti, alloy thereof, or non-metal such as carbon.The thickness of the first conductive layer 90 and the second conductivelayer 92 may be 0.001 um to 1 mm.

Continuing the above description, the drive mechanism of the gripperunit described in the second embodiment of the present invention may beapplied to the EUV mask with the first conductive layer and the secondconductive layer. As shown in FIG. 12a , when the reciprocating member46 works to make the third rolling member 94 to move substantially alongthe third direction 98 and the fourth rolling member 96 movesubstantially along the fourth direction 100, the head portion 422 ofthe gripper unit 42 moves toward the opposite direction of the thirddirection 98 and the grounding pin 50 moves toward the oppositedirection of the fourth direction 100 so that the head portion 422 andthe grounding pin 50 are led away from the EUV mask 10. As shown in FIG.12b , when the reciprocating member 46 works to leave from the thirdrolling member 94 and the fourth rolling member 96, the head portion 422of the gripper unit 42 moves toward the third direction 98 by means ofthe third force of the third resilient member 102 and an upper portionof the arm structure 44 moves toward the fourth direction 100 by meansof the fourth force of the fourth resilient member 102′ so that the headportion 422 is therefore led toward the edge of the EUV mask 10 and inthe end to abut against the EUV mask 10, and the grounding pin 50contacts the second conductive layer 92 of the EUV mask 10 to dischargethe charge on the reflective surface 16 of the EUV mask 10.

On the other hand, the grounding pin controlling structure 60 describedin third embodiment of the present invention may also be applied to theEUV mask 10 with the first conductive layer 90 and the second conductivelayer 92 thereon. As shown in FIG. 13a , during the inspection of theEUV mask 10, the column 64 moves up and the grounding pin 50 contactsthe second conductive layer 92 of the EUV mask 10. After the inspectionof the EUV mask 10, as shown in FIG. 13b , the column 64 moves down andthe grounding pin 50 is far away from the EUV mask 10. The embodimentsof the grounding pin controlling structure 60 are described above, andunnecessary details would not be given here.

Furthermore, as shown in FIG. 14, the grounding pin may be a spring 110with a trigger 112 on the top end of the spring 110, and the bottom endof the spring 110 is grounded. When the EUV mask 10 moves to beinspected, the second conductive layer 92 of the EUV mask 10 may contactwith the trigger 112 by the weight of the EUV mask 10 to discharge thecharge on the reflective surface 16 of the EUV mask 10.

In another embodiment, the grounding pin is used to contact at least oneconductive layer on one side of the EUV mask. As shown in FIG. 15a andFIG. 15b , a conductive layer 93 is formed on one corner of the EUV mask10, the two adjacent side walls 105, 105′, accordingly, and theconductive layer 93 is electrically connected to the reflective surface16 of the EUV mask 10. The structure for discharging EUV mask includes aconductive holder 130 with the grounding pin 50, as shown in FIG. 16, toclamp the corner of the EUV mask 10, so that the grounding pin 50 maycontact with the conductive layer 93. Refer to FIG. 16, two groundingpins 50 are respectively formed on a pair of opposite clamp sections 131of the conductive holder 130, so that the two grounding pins 50 maycontact the conductive layer 13 at two adjacent side walls 105, 105′ ofthe EUV mask 10.

Further, as shown in FIG. 17, two trenches 132 or notches arerespectively formed on two adjacent side walls 105, 105′ of the EUV mask10, and a conductive layer 93 formed on the trenches 132 or the notchesis electrically connected to the reflective surface 16 of the EUV mask10. Here, the profile of the trenches 132 or notches may correspond tothe grounding pins 50 arranged on the conductive holder 130 as shown inFIG. 16, so that the grounding pin 50 may closely contact the conductivelayer 93.

Furthermore, as shown in FIG. 18, the foregoing conductive layer 93 maybe formed on the whole side wall, including the trenches 132 or thenotches walls, of the EUV mask 10, so that the grounding pin 50 maycontact with the conductive layer 93 conveniently. The coated conductivelayer 93 may be Al, Cr, Ti, alloy thereof, or non-metal such as carbon.The thickness of the conductive layer 93 may be 0.001 um to 1 mm.

FIG. 19 is a flow chart illustrating a method for inspecting an EUV maskby using a charged particle beam according to an embodiment of thepresent invention. In step of S110, a grounding pin slightly contacts tothe EUV mask while the EUV mask is positioned. Here, the grounding pincan contact the reflective surface, backside surface, or sidewallsurface of the EUV mask to achieve a discharging effect. In step ofS120, a stage, for supporting the EUV mask, is moved continuously, andthe reflective surface of the EUV mask is scanned by using a chargedparticle beam simultaneously. Furthermore, the moving direction of thestage is perpendicular to the scanning direction of the charged particlebeam. The charged particle beam, in one embodiment, is electron beam. Instep of S130, signal electrons emanated from the reflective surface ofthe EUV mask can be received by a detector to form an imaging. Here, thesignal electrons can be secondary electrons or backscattered electrons.

FIG. 20 shows a low voltage scanning electron microscope (LVSEM) used toinspect a EUV mask. In this figure, an objective lens can be a SORILoptical system.

In this embodiment of the scanning electron microscope 300, the electronbeam 304 emitted from a cathode 302 is accelerated by an anode 306voltage, passes through a gun aperture 308, a condenser lens 310, a beamlimit aperture 312 and a SORIL system 316, and then impinges onto aspecimen surface 326 supported by a stage 328.

When a fixed negative potential Vc and a potential Va, which is enoughhigher than Vc, are respectively applied to the field emission cathode302 and the anode 306, the electron beam 304 is emanated from thecathode 302 along an optical axis. The emanated electrons are firstlyaccelerated in the space between the cathode 302 and anode 306, and thendecelerated (accelerated or remain even speed in some cases) in thespace between the anode 306 and a terminal electrode at groundpotential.

Because the gun aperture 308 is closer to the electron source, theelectron beam 304 with larger polar angles can be cut off by the gunaperture 306, and trimmed down to a specific current value. It can alsobe earlier to prevent from the Coulomb interaction of the electron beam.Then the electron beam 304 passes the condenser lens 310 and the beamlimit aperture 312. The condenser lens 310 can weakly condense theelectron beam 304. The beam limit aperture 312 can determine the amountof the electron beam 304 to a desired beam current on the specimen 326,and allow entering the objective lens system 316 with a fixed energy, afixed brightness and a fixed beam current.

The SORIL system 316 includes an objective lens 318, deflectors 320 and322 which are located inside the objective lens 318, and a controlelectrode 324. The objective lens 318 can be an immersion electrostaticobjective lens, an immersion magnetic objective lens, or anelectromagnetic compound objective lens. In the embodiment, theimmersion magnetic objective lens 318 is more preferred. The immersionmagnetic objective lens 318 can focus the electron beam 304 into a smallspot which is used to scan the studied specimen 326. Because focusingthe electron beam 304 is mainly accomplished by the magnetic objectivelens 318, the aberrations of the beam spot mostly come from thespherical aberration and the chromatic aberration of the magneticobjective lens 318. The purpose of the immersion magnetic objective lens318 is to generate a magnetic field with a large component perpendicularto the Z-axis for converging lens action above the specimen 326 and tohave the magnetic field substantially parallel to the Z-axis at thespecimen 326. Accordingly, the specimen 326 can be immersed in themagnetic field of the lens.

The deflection units 320 and 322 in the SORIL system 316 can be equippedwith electrostatic multi-pole deflectors or magnetic multi-poledeflectors. The embodiment is more preferred the electrostaticmulti-pole deflectors because the magnetic multi-pole deflectors wouldproduce magnetic hysteresis phenomenon on deflecting the electron beam304 during operation. Therefore, it would affect the scanning speed. Theelectron beam 304 can be deflected by the deflection units 320 and 322which can generate a small deflection field, or can work together withthe control electrode 324 to increase the size of the deflection field,so that the specimen 326 can be scanned by the focused beam.Furthermore, the deflection units are designed to minimize theintroduction of aberrations into the beam when deflecting the electronbeam. In accordance with the embodiment, the deflection units 320 and322 are dedicated to produce a more rapid scanning movement of theelectron beam 304 to cover a suspected region, and it can enhance thethroughput of the imaging.

The control electrode 324 is made of electrical conduction material. Thecontrol electrode 324 is shaped and positioned to be an extension ofouter polepiece of the magnetic objective lens 318 towards optical axis.The control electrode 324, on one hand, is set to a voltage Vce tocontrol the electrical field on the specimen surface 326 lower than thepredetermined value, which ensures on micro-arcing on the specimensurface 326. On the other hand, the voltage Vce of the control electrode324 can be dynamically adjusted to compensate the image defocus due toelectric drifting.

Since an imaging with better quality can be obtained through theelectron beam 304 impinging on the specimen surface 326, the systemneeds to make every component's applied voltage and excitation currentsynchronize. Any electric drifting on these components will cause thespot size of the electron beam 304 varied and defocus of the image. Thecontrol electrode 324 can be dynamically performing micro-focusing whilethe image is defocused. The control electrode 324 can increase themagnetic field strength of the SORIL system 316 under a same excitation.Placing the control electrode 324 in the retarding field gives thecontrol electrode 324 a great deal of influence over the trajectory ofthe electron beam 304 because the electron beam 304 has been reduced toa lower landing energy than the deflection units 320 and 322, and it isnearest the landing point of the electron beam on the specimen 326.Furthermore, because of its proximity to the specimen 326, it can helpto accurately position the electron beam 304 over a selected area of thespecimen 326 prior to the rapid scan of the area, and improve the sizeof the deflection field over the specimen 326.

The SORIL system 316 adopted in the embodiment is preferred because itcan reduce the off-axis chromatic and spherical aberrations greatly inscanning imaging, and is better at extending its magnetic field belowthe lens aperture and through the specimen 326 to increase the field ofview.

To reveal a stereo imaging of the specimen surface 326 with betterimagine quality, the embodiment of the present invention can adopt themulti-channel detector 314 to collect the signal electrons during thescanning operation. The signal electrons, including the secondaryelectrons or the backscattered electrons, emanated from the differentsides or features of the specimen surface 326 can be collected bydifferent channels. Therefore, the signal electrons from the differentemanated directions can generate a stereo image in combination, andfinally ensure a topography analysis of the defects of interest regions.

The specimen 326 on the specimen stage 328 is charged with a negativevoltage to create a retarding field Er; that is, a field in the oppositedirection to the accelerating field Ea to reduce the energy of theelectron beam prior to impact with the specimen 326, and avoid greatdamage of the specimen surface. Furthermore, the retarding field canmake the electron beam 304 land on the specimen surface with a lowerlanding energy.

FIG. 21 shows a schematic diagram of a structure 500 for an electronbeam inspection system processing continuous scanning on a EUV mask. Theelectron beam inspection system adopts the LVSEM disclosed in the FIG.20, and is expressed in a simplified manner.

A stage 522 on the inspecting system is used for supporting the EUV mask520. The reflective surface of the EUV mask 520 is continuously scannedby using the electron beam 504 when the stage 522 moves continuously atthe same time. The stage 522 can move along the direction 526 and thesurface of EUV mask 520 can be scanned by the electron beam 504 underthe control of the first deflector 514 and the second deflector 516. Themoving direction of the stage is perpendicular to the scanning directionof the electron beam. When the EUV mask 520 is inspected by using theelectron beam 504, it should be grounded simultaneously.

And the signal electrons emanated from the surface of the EUV mask 520would be received by a detector 512.

No matter the grounding pin is contacted with the reflective surface,the bottom conductive layer or the side conductive layer, the presentinvention provides a structure to discharge the EUV mask duringinspection by an E-beam inspection tool, so that non accumulatedcharging is on the EUV mask during E-beam inspecting to enhance theinspection quality.

In the present invention, when applying the foregoing structure todischarge the EUV mask to an electron beam inspection system, theelectron beam inspection system for inspecting an EUV mask includes: anelectron gun for providing electron beam; a lens for focusing theelectron beam on the EUV mask; a detector for receiving signal electronsemanating from the EUV mask; and means for discharging the EUV maskduring the EUV mask is inspected; the reflective surface of the EUV maskon a continuous moving stage is scanned by using the electron beamsimultaneously under the control of the first deflector and seconddeflector; the movement direction of the stage is perpendicular to thescanning direction of the electron beam. The inspection quality of theEUV mask is enhanced by using the electron beam inspection systembecause the accumulated charging on the EUV mask is grounded.

Although the present invention has been explained in relation to itspreferred embodiment, it is to be understood that other modificationsand variation can be made without departing the spirit and scope of theinvention as hereafter claimed.

What is claimed is:
 1. A method for inspecting an EUV mask by using a charged particle beam, wherein the EUV mask comprises a reflective surface, and the reflective surface comprises a patterned reflective surface area and a peripheral area, the method comprising: grounding the EUV mask via the peripheral area, wherein the peripheral area is electrically connected to the patterned reflective surface area; moving continuously a stage, wherein the stage is for supporting the EUV mask, and simultaneously scanning the patterned reflective surface area of the EUV mask by using the charged particle beam; and receiving signal electrons emanated from the patterned reflective surface area of the EUV mask.
 2. The method for inspecting an EUV mask by using a charged particle beam according to claim 1, wherein the charged particle beam is an electron beam.
 3. The method for inspecting an EUV mask by using a charged particle beam according to claim 2, wherein a stage's moving direction is perpendicular to a scanning direction of the electron beam.
 4. The method for inspecting an EUV mask by using a charged particle beam according to claim 3, wherein the EUV mask is inspected by a low voltage scanning electron microscope.
 5. The method for inspection an EUV mask by using a charged particle beam according to claim 4, wherein said step of grounding the EUV mask is performed by slightly contacting a grounding pin to the reflective surface of the EUV mask.
 6. The method for inspection an EUV mask by using a charged particle beam according to claim 4, wherein said step of grounding the EUV mask is performed by contacting a grounding pin to a back surface of the EUV mask, and a conductive layer is on the back surface of the EUV mask and electrically connecting to the reflective surface of the EUV mask.
 7. The method for inspection an EUV mask by using a charged particle beam according to claim 6, wherein the grounding pin contacts the back surface of the EUV mask slightly.
 8. A system for inspecting an EUV mask, wherein the EUV mask comprises a reflective surface, and the reflective surface comprises a patterned reflective surface area and a peripheral area, the system comprising: a source for providing an electron beam; an objective lens for focusing the electron beam on the patterned reflective surface area of the EUV mask; a detector for receiving signal electrons emanated from the patterned reflective surface area of the EUV mask; a stage for supporting the EUV mask; and means for grounding the EUV mask via the peripheral area, wherein the peripheral area is electrically connected to the patterned reflective surface area, wherein the patterned reflective surface area of the EUV mask is scanned by the electron beam when the stage moves continuously.
 9. The system for inspecting an EUV mask according to claim 8, wherein a stage's moving direction is perpendicular to a scanning direction of the electron beam.
 10. The system for inspecting an EUV mask according to claim 9, wherein the system is a low voltage scanning electron microscope.
 11. The system for inspecting an EUV mask according to claim 10, wherein said means for grounding the EUV mask includes a grounding pin slightly contacting the reflective surface of the EUV mask.
 12. The system for inspecting an EUV mask according to claim 10, wherein said means for grounding the EUV mask includes a grounding pin contacting a back surface of the EUV mask, and a conductive layer is on the back surface of the EUV mask and electrically connecting to the reflective surface of the EUV mask.
 13. The system for inspecting an EUV mask according to claim 12, wherein the grounding pin contacts the back surface of the EUV mask slightly. 